1. Field of the Invention
The present invention relates to a zoom lens capable of image stabilization and an imaging apparatus, and more particularly to a zoom lens capable of image stabilization and an imaging apparatus equipped with the same, which are suitably used for a video camera or digital camera, particularly a 3 CCD video camera using three CCDs, so as to obtain a good image by moving a lens group of a part of a variable magnification optical system in a direction approximately orthogonal to an optical axis and optically correcting blurring of a taken image occurring when the variable magnification optical system vibrates (or tilts).
2. Description of Related Art
In imaging on a moving object such as a vehicle or handheld imaging under a condition of slow shutter speed, a taken image is blurred due to a hand shake when vibrations are transferred to an imaging optical system.
For this reason, an optical system capable of image stabilization, which has a function for preventing blurring of a taken image due to vibrations of the imaging optical system, has been variously proposed.
There is a well-known optical system for promoting image stabilization by moving a part of a lens group of an imaging optical system in a direction approximately orthogonal to an optical axis (for example, see Japanese Patent No. 3557344). The technique disclosed in Japanese Patent No. 3557344 includes a positive first lens group fixed in varying magnification, a negative second lens group having a variable magnification function, a positive third lens group fixed in varying magnification, and a positive fourth lens group having both a correction function for correcting an image plane variation with varying magnification and a focusing function, arranged in this order from the object side. When the variable magnification optical system vibrates, blurring of a taken image is corrected by moving the third lens group fixed in varying magnification in the direction approximately orthogonal to the optical axis for image stabilization.
However, in the above-described technique, the load of a lens drive system is heavy since the entire third lens group moves. In particular, in the zoom lens of a four-group constitution having positive, negative, positive and positive components corresponding to a 3 CCD system, the refractive power of the third lens group is relatively low to obtain a long back focus and a movement amount for image stabilization of a blurring correction group is necessarily large, such that the load of the lens drive system becomes heavier.
As described in the techniques of JP-A-11-237550, JP-A-2000-298235 and Japanese Patent No. 3359131, it is known that one group of a plurality of groups constituting the third lens group moves for image stabilization. In the JP-A-2000-298235, a five-group constitution of positive, negative, positive, negative and positive components in this order from the object side is disclosed. However, since a space between third and fourth groups is not varied in varying magnification and a combination of these two groups has positive refractive power as clearly shown in a conditional expression, the zoom lens having a four-group constitution of positive, negative, positive and positive components can be assumed.
As described above, the load of the lens drive system may be significantly reduced by moving one group of a plurality of lens groups constituting the third lens group without moving the entire third lens group for image stabilization. In particular, this is extremely effective in a zoom lens having a four-group constitution of positive, negative, positive and positive components corresponding to the 3 CCD system.
However, in JP-A-11-237550, the third lens group is formed by arranging a negative lens group and a positive lens group in this order from the object side and the positive lens group arranged on an image side is operable for image stabilization, such that a light flux is spread at a position of the positive lens group according to light flux divergence of the negative lens group of the object side and the positive lens group driven for image stabilization has an increased size and an increased weight. Consequently, there is a problem in that it is difficult to perform quick vibration isolation control at low power. At present, a small size and low power consumption are strongly required in a video camera or digital camera and the development of a lens system capable of performing quick vibration isolation control is required.
In JP-A-2000-298235, the third lens group is formed by arranging a negative lens group and a positive lens group in this order from the object side and the positive lens group arranged on the object side is operable for image stabilization. However, when the positive lens group moves for image stabilization, the refractive power of the positive lens group should be higher to suppress its movement amount, such that it is difficult to perform a sufficient aberration correction at the time of a blurring correction.
Also in embodiments described in Japanese Patent No. 3359131, the third lens group is constituted with a positive lens group and a negative lens group. There is the same problem as those of JP-A-11-237550 and JP-A-2000-298235 since the positive lens group moves in the direction approximately orthogonal to the optical axis for image stabilization.